Olivine Group of Minerals

In the earlier article we have discussed different groups of minerals, like Mica, Amphibole, Pyroxene, Quartz group of minerals. This is another important group of minerals, which include a series of minerals that crystallize in the orthorhombic system. These minerals range in composition from ”forsterite” Mg2 SiO4. The composition of common Olivine is (Mg,Fe)2 SiO4.

List of Contents

Properties of Olivine: (Mg, Fe)2 SiO4

Crystal System: Olivines have an Orthorhombic crystal system.
Fracture: Olivines are found in Conchoidal fracture.
Hardness: Olivines have a hardness of 6.5-7 on Moh’s scale.
Sp.gr: It has specific gravity equal to 3.27-4.37.
Lustre: Olivine group of minerals have a vitreous lustre.
Colour: Minerals of olivine group have pale, yellow green or olive green.
Habit: Granular.
Streak: Olive green to brown.
Tenacity: Brittle
Cleavage: Poor/Indistinct.
Density: 4.46 g/cm³ (Measured) 4.45 g/cm³ (Calculated).

What physical properties of minerals include?

Occurrence:

Olivine occurs mainly in the dark coloured igneous rocks such as gabbro, periodotite and basalt. The rock, dunite is made up almost wholly of olivine. Olivine alters very readity to serpentine.

Minerals of Olivine Species:

Dunite

Solid, grainy masses of Olivine. Usually classified as a rock.

Olivenoid

Extraterrestrial form of Olivine found in meteorites.

Peridote

Fe₂Mg₈O₂₀Si_5,Transparent green variety of Olivine that is used as a popular gemstone.

Calcio-olivine

Ca₂SiO₄

Fayalite

Fe²⁺₂SiO₄

Forsterite

Mg₂SiO₄

Glaucochroite

CaMn²⁺SiO₄

Kirschsteinite

CaFe²⁺SiO₄

Laihunite

(Fe²⁺_0.5◻_0.5)Fe³⁺[SiO₄]

Larnite

Ca₂SiO₄

Liebenbergite

Ni₂SiO₄

Monticellite

CaMgSiO₄

Tephroit

Mn²⁺₂SiO₄

Uses of Olivine Minerals:

Olivine is used in metallurgical process as a slag conditioner (A slag conditioner containing MgO, carbon or a filler and a binder is mixed and formed under pressure to produce aggregates which can have the form of a briquette. The slag conditioner is used to improve the operating performance and refractory life in steel melting furnaces).
Forsterite (a magnesium rich olivine) is added to blast furnaces to remove impurities from steel and to form a slag.
Olivine is used as refractory material, and casting sand, while making refractory bricks (ceramic bricks/ tiles). But usage of olivine as refractory material is not a cheap source, which is why it is gradually being replaced by other cheaper materials.
Olivine is resembles to ”peridote”, which is used in jewelry and has metaphysical importance. As peridote is expensive, therefore, Olivine is used as peridote substitutely.
Bricks made up of Olivine refractory material are used in construction of stoves and furnaces because of its high resistivity against heat and high temperatures.
Olivine refractory material is used in bricks to reduce the weathering caused by continuous heating and cooling of the walls of stoves.

Countries rich with Olivine Minerals:

Olivine is found abundantly in igneous rocks of following geographic regions;

Ultramafic intrusions (e.g., Norway, Germany);
Ophiolite complexes (e.g., Greece, Italy, Turkey);
Alpine peridotites (ophiolite or subcontinental mantle) emplaced along thrust faults (e.g., Italy, Spain);
Rift zones/basalts of mid-ocean ridges (e.g., Iceland);
Volcanic xenoliths (e.g., German Eifel and Kaiserstuhl, Iceland).
A melilite–olivine nephelinite lava flow occurring in Hamada, SW Japan.